Alternative fuel gasses, such as natural gas and hydrogen, are promising alternatives to the traditional petroleum-based energy sources used in automotive vehicles. They are cleaner burning than petroleum-based gasoline and diesel, and are therefore better for the environment. Two prevailing technologies exist for storing fuel gasses aboard a vehicle—in a compressed state or on a gas storage material. Compressed natural gas, for example, is stored at high pressure to less than 1% of the volume it would normally occupy at standard temperature and pressure. Natural gas can also be stored on a storage material (ANG storage material) in an adsorbed state. The allure of such ANG storage materials is that can reversibly adsorb natural gas at an energy density comparable to compressed natural gas but at a much lower tank pressure.
In ANG technologies, example ANG storage materials include activated carbon, metal-organic-frameworks (MOFs), and porous polymer networks (PPNs). The ANG materials are commonly contained in a vehicle storage tank that is filled and refilled with natural gas for adsorption. One issue presented during refilling events involves the susceptibility of certain ANG materials to degradation. Some contaminants have been shown to decrease the adsorption capabilities of the ANG materials, among other possible adverse effects. Contaminants encountered when refilling vehicle storage tanks with natural gas include moisture, dust from aged pipelines, oils and lubricants from prior processing equipment like compressors, and potentially other matter. Filters have been employed in upstream equipment, such as natural gas dispensers, to remove the contaminants from the refilled natural gas before the gas enters the vehicle storage tanks. But the filtering constructions to date exhibit shortcomings that make them undesirable and unsuitable in certain applications.
Storing hydrogen gas on a hydrogen storage material has similar thermodynamics to storing natural gas on an ANG storage material even though hydrogen uptake is chemical in nature—hydrogen is stored as a hydride—as opposed to adsorptive. Hydrogen gas, for instance, can be reversibly charged and released from a hydrogen storage material such as, for example, a complex metal hydride including various known alanates, borohydrides, and amides. Some specific complex metal hydrides include sodium alanate (NaAlH4), lithium alanate (LiAlH4), lithium borohydride (LiBH4) with or without MgH2, calcium borohydride (CaBH4) with or without MgH2, and lithium amide (LiNH2). MOFs and PPNs may also be used to store hydrogen gas. There are, of course, many other hydrogen storage materials that are commercially available. And, much like with ANG storage materials, hydrogen storage materials can be susceptible to a decline in hydrogen uptake capabilities if exposed to contaminants such as, for example, hydrogen sulfide, which may find their way into the hydrogen gas flow being delivered to the hydrogen gas storage tank that houses the hydrogen storage material.